Many known fluid handling devices employ a movable fluid flow controlling member biased by a spring. Valves in particular frequently employ such construction, the movable member comprising a valve element biased toward engagement with a mating seat by the spring. In valves employed in fuel injectors in automotive fuel injection systems, the valve element and spring are typically arranged within a housing such that the valve element remains seated and the valve closed under the bias of the spring until the force from fluid at predetermined, critical pressure within the injector overcomes the spring bias and the valve opens. In automotive fluid injectors, uniformity in the critical opening pressure of all the injectors within a single system is imperative. To achieve such uniformity within the limits of normal dimensional and metallurgical variations in the component parts which make up an injector, it is a common practice to adjust the injector as it is assembled to open at the desired critical pressure. A common method of making such an adjustment involves the preloading (adjusting the length) of the spring which maintains the seating of the injector valve by means of shimming the spring, thereby increasing the seating force applied to the valve element by the spring. Heretofore, such adjustment required testing each fuel injector to determine its characteristic opening pressure and then disassembling of the injector, shimming the spring, reassembling the injector and retesting thereof, the size of the shims being determined primarily by guesswork on the part of the assembler. As those skilled in the art of valve assembly will appreciate, to achieve a precise opening pressure, it may be necessary to repeat the shimming procedure set forth hereinabove, a number of times until the required shim thickness are determined. It will also be appreciated that such trial and error techniques are time consuming, costly and do not lend themselves to the automated assembly of such components.